The present invention is related to the invention described in copending application Ser. No. 11/860,759, filed concurrently herewith and titled CONTROL METHOD AND BALLAST FOR RUN-UP OF METAL HALIDE LAMP that is incorporated herein by reference.
The present invention is directed to a method of decreasing the time from ignition to nominal (full) light output of a metal halide lamp.
Metal halide lamps for general lighting are efficient and produce high quality white light. However, the lamps require a few minutes to warm up to nominal light output because ballast output is focused mainly on steady-state operation. Shorter times to nominal light output would improve the applicability of metal halide lamps.
A faster run-up to steady state lamp operation can be achieved by overpowering a cold lamp. A temporarily high power level is not necessarily a problem, but because a cold lamp also tends to have a very low voltage, an excessively high current would be required to achieve the power needed (power=voltage×current). Moreover, care must be taken because excessive power or current can lead to thermal shock, electrode damage, and wall blackening, and lamps typically have a current limit during run-up to avoid these problems. Thus, light output does not reach nominal as quickly as desired.
Power modulation of a metal halide lamp is known. See, for example, U.S. Pat. No. 6,229,269 in which power modulation is used to bend the arc of the lamp to increase the length of the arc and the voltage; U.S. Pat. No. 6,124,683 in which acoustic modulation is used to allow the lamp to be oriented vertically; and U.S. Pat. No. 5,684,367 in which amplitude modulation and pulsing of the input power waveform control color characteristics and arc stability.